已知$\left|\overrightarrow{a}\right|=1,\left|\overrightarrow{b}\right|=3,<\overrightarrow{a},\overrightarrow{b}>={60}^{°},(\overrightarrow{a}-\overrightarrow{c})(\overrightarrow{b}-\overrightarrow{c})=0,$则$\left|\overrightarrow{c}\right|$的最小值是(     )

氢氧化钠是一种重要的化工原料，工业上常用电解饱和食盐水的方法来制取烧碱、氯气（Cl₂）和氢气．

（1）写出工业上电解饱和食盐水的化学方程式____ ．

（2）如图所示，小田同学在进行酸碱中和反应的实验时，向烧杯中的氢氧化钠溶液滴加稀盐酸一会儿后，发现忘记了滴加指示剂．为了确定盐酸与氢氧化钠是否恰好完全反应，小田从烧杯中取了少量反应后的溶液于一支试管中，并向试管中滴加几滴无色酚酞试液，振荡，观察到酚酞试液不变色．于是她得出“两种物质已恰好完全中和”的结论．

①你认为她得出的结论是否正确____ （填“正确”或“不正确”），理由是____．

②请你设计一个实验，探究上述烧杯中的溶液是否恰好完全中和（写出实验步骤、实验现象及结论）____ ．

     Roger Scott worked as a salesman in a department store. Like a lot of other young people, he didn't like his  1   very much. One day he was   2 in the canteen (食堂)of the store with his girlfriend, Annie Davis. She worked there, too. "I'm going to find another job as soon as I    3". He said, “The pay isn't very good and the work isn't interesting, either. The worst thing with it is that I have to take orders from people like Mr. Smith! Mr. Smith was the manager of the store. Everybody was  4 afraid of him. He often walked around the store and always got very angry if he saw somebody who was not working. Sometimes there was really no work to do  5people still tried to look busy.
While Roger was talking, Annie looked up and saw Mr. Smith  6 into the canteen. Roger was sitting near the door and Mr. Smith was just behind him. He could hear what Roger was telling. Annie didn't know what to do. "I  7  Mr. Smith is even a very good manager." Roger continued loudly. "  8 a man is a good manager, the people would  9to work for him. I'm sure everyone here hates it! At least I am." Annie saw Mr. Smith come closer. There was a very angry    10 on his face.

某欧姆表的内部结构如图甲所示电路，欧姆表开关拨至“ ”，并进行了必要的调零。一同学准备用一个电阻箱R_x较精确地测出欧姆表的电源的电动势E和该倍率下完成调零后欧姆表的内阻 ，他的操作步骤是：

a．将欧姆表与电阻箱R_x连成图甲所示的闭合电路；

b．调节电阻箱阻值，记下电阻箱示数R_x和与之对应的电流表G的示数I；

c．将记录的各组R_x、I的数据描点在图乙中，得到 图象；

d．根据图乙作得 的图象，求出电源的电动势E和欧姆表内阻R_内。